1. Field of the Invention
This invention relates to a layout tool for measuring inclination of objects, and for rapidly determining the complementary angle of inclination and the perpendicular to the given angle of inclination. More particularly, the invention relates to a wood framing layout tool and method for indicating and scribing for angular cuts to be made in roof rafters.
2. Material Art
A number of framing layout tools have been utilized to assist professional and amateur carpenters in particular for roof framing construction. During the construction of roofs or other structures using inclined members, it is necessary to perform a series of accurate angular cuts on these members to allow them to fit into place with a minimum of error, thus enhancing their structural integrity. The required cuts on a typical roof rafter are shown in FIG. 1. The inclinations involved are most often expressed in terms of rise-over-run e.g., "4 in 12" means a rise of 4 inches over a horizontal distance of 12 inches. Carpenters think in these terms when dealing with inclination.
The layout of these cuts is most often performed with a carpenter's square--a square with graduations on each edge which allow the user to set the tool to whatever rise-over-run inclination is desired. Typically the required inclination would be determined by the plans for the structure. There are any number of variations on the carpenter's square commonly available.
The process of remodeling offers a different set of challenges to the carpenter. Instead of having a set of plans to work from, the remodeler is typically faced with the task of matching an existing inclination which will usually not be an exact, nominal, rise-over-run inclination. Further, from naturally caused changes such as settling and earthquakes the inclinations of the rafters may have changed. There currently exist a number of devices for measuring the inclination of a member. Perhaps the most common type is the bevel-square, a device which allows the user to `capture` the angle between the given member and another adjacent member without actually measuring the angle. This tool allows the angle to be transferred only. A serious limitation of the bevel square is that it requires the members to be adjacent for a measurement to be taken. Often, access to only the inclined member is available, rendering the tool useless.
A second class of devices use a bubble-vial type level in conjunction with one or more measuring blades and graduated scales. Some of these tools allow the user to determine the angle of inclination only with respect to the horizontal. Many of them also have means for locking the measurement for future transfer without resetting. An available device is the Squangle tool U.S. Pat. No. 3,289,301 where a straight slotted bar is pivotably pin connected at one end to a slotted L-shaped blade, the respective slots containing a common slidable and clampable second pin. A bubble-vial level is recessed in a linear edge of the slotted bar at a bar end opposite to the first pin connection. The patent document shows a second transverse bubble-vial. A serious limitation of these devices is caused by the use of the bubble-vial level. Due to the nature of the measurement situation, these tools are often used in positions which make the reading and accurate interpretation of the level vial difficult or impossible.
A third class of devices comprises an electronic level with digital angle readout as exemplified by the Smart Level.TM. available from WEDGE Inventions, Santa Clara, Calif. and the INOGON.RTM. angle indicator U.S. Pat. No. 3,945,129 available from Borel & Dummer, Inc. of Novi, Mich. marked U.S. Pat. No. 3,945,129. These tools allow the user to measure the inclination of any member in any orientation. The main drawback to these devices is that once the inclination is known, the information must then be transferred to a traditional layout tool such as the carpenter's square to perform the layout. An additional limitation arises from the fact that the inclination of an existing member is seldom a precise integer rise-over-run (e.g., 2/12.3/12, . . .). The level will measure the angle with resolution on the order of 0.2 or 0.1 degree. The framing layout tool to which this number must be transferred, however, does not have any such resolution. They generally have only integer rise-over-run markings, and thus a loss in accuracy arises in transferring the actual inclination to the layout.